The prevalence of diabetes and its associated vascular complications have been assessed in several Pacific Island populations, including Polynesians and Melanesians, living in traditional ways as well as in urbanized communities. In general, much higher prevalences of diabetes and the associated complications were found in the urbanized populations, and attempts to determine the reasons for these differences are being pursued. Increased obesity, reduced physical activity, changes in dietary composition and intake appear to contribute to these differences in frequency, but genetic factors also are likely important in determining the frequency of the diabetes, itself, and possibly the type and frequency of associated complications. Identification of the relative importance of environmental determinants of diabetes is a prerequisite to formulating preventive measures for this disease in developing countries.